Although the possibility of treating rheumatoid arthritis, other inflamed joints, and cancer with yttrium-90 (.sup.90.sub.39 Y) is well known, a cost effective way to separate .sup.90 Y of sufficient purify that minimizes loss of radioactive Sr and does not generate a large waste stream is still needed. .sup.90 Y results from the decay of strontium-90 and .sup.90 Y decays to stable .sup.90 Zr according to the following scheme: ##EQU1##
.sup.90 Y has a relatively short half-life (64.0 h) and maximum beta energy (2.28 MeV) which makes it suitable for a variety of therapeutic uses such as radiolabeling antibodies for tumor therapy or treating liver malignancies.
Although it is known that .sup.90 Y is suitable for immuno radiotherapy, scientists and doctors have encountered numerous difficulties using .sup.90 Y for medical treatments because of the absence of a cost effective way to separate .sup.90 Y of sufficient purity while minimizing loss of radioactive Sr without generating a large waste stream. The following non-exclusive non-exhaustive list of difficulties in separating and purifying .sup.90 Y have limited the application of .sup.90 Y for medical treatment. Although the half-life and decay scheme of .sup.90 Y is appropriate for various radio therapy applications, .sup.90 Y must be capable of being produced in sufficient multi-curie quantities. Furthermore, before .sup.90 Y can be safely used in clinical applications, .sup.90 Y must be essentially free of .sup.90 Sr and any other trace elements. .sup.90 Y must be free of .sup.90 Sr by at least a factor of 10.sup.7 because .sup.90 Sr can suppress bone marrow production. .sup.90 Y must also be free from any trace elements, such as Ca, Cu, Fe, Zn, and Zr, and other impurities because trace elements could interfere with the radio labeling process by competing with .sup.90 Y for binding sites. All of these difficulties must be overcome in a cost effective manner while minimizing loss of valuable radioactive Sr without generating large amounts of waste.
In the past, .sup.90 Y has been separated from .sup.90 Sr by solvent extraction, ion-exchange, precipitation, and various forms of chromatography, all of which fail to separate .sup.90 Y of sufficient quantity and purity in a cost effective manner that minimizes loss of radioactive Sr and does not generate a large waste stream. Numerous procedures use a cation exchange resin (e.g. Dowex 50) to retain .sup.90 Sr, while the .sup.90 Y is eluted with an aqueous solution such as lactate, acetate, citrate, oxalate, or EDTA. Several of these procedures have been proposed as the basis for a .sup.90 Y generator system.
U.S. Pat. No. 5,100,585, and U.S. Pat. No. 5,344,623 describe processes for recovering strontium and technetium from acidic feed solutions containing other fission products.
Another process for separating .sup.90 Y from .sup.90 Sr involves extracting .sup.90 Y from a dilute acid solution of .sup.90 Sr/.sup.90 Y using bis 2-ethylhexyl phosphoric acid in dodecane. This procedure has the disadvantages of having a limited generator lifespan and accumulating radiolytic by-products in the .sup.90 Sr stock. This process also has the disadvantage of requiring repeated stripping of the initial extractant solution to reduce trace impurities and repeated washing of stock solution to destroy dissolved organic phosphates.
Kanapilly and Newton (1971) have described a process for separating multi-curie quantities of .sup.90 Y from .sup.90 Sr by precipitating .sup.90 Y as a phosphate. This process, however, requires adding nonradioactive yttrium as a carrier, yielding .sup.90 Y which are obviously not carrier free and hence unsuitable for site specific binding. This and other prior art teach the addition of only nonradioactive yttrium. This and other prior art do not teach the addition of nonradioactive strontium. In fact, the prior art teaches away from adding nonradioactive strontium.
U.S. Pat. No. 5,368,736 describes a process for isolating .sup.90 Y from a stock solution of .sup.90 Sr. The .sup.90 Sr solution is stored for a sufficient period of time to allow .sup.90 Y ingrowth to occur. This process teaches the use of a series of Sr selective columns at the initial stages of the process. A major disadvantage is that .sup.90 Sr must be stripped off from each of the strontium-selective extraction chromatographic column because .sup.90 Sr is very valuable and it must be recycled to allow for new .sup.90 Y growth.
Unfortunately, all the various methods mentioned above suffer from one or more of the following disadvantages. The first disadvantage of these methods is that the concentration of trace elements is too high and the trace elements thereby compete with .sup.90 Y for binding sites, resulting in a decrease in .sup.90 Y labeling. Thus, it is necessary to either remove trace elements and other impurities prior to antibody labeling or carry out postlabeling purification. The second disadvantage is that ion-exchange resins gradually lose capacity due to radiation damage. As a result, ion-exchange is considered suitable only for purifying and separating subcurie quantities of .sup.90 Y, which is less than the multi quantities of .sup.90 Y needed for clinical applications. The third disadvantage is that separating .sup.90 Y in acceptable purity and quantity while minimizing .sup.90 Sr breakthrough often requires using a series of long ion-exchange columns and impractically large volumes of eluent. A need still exists for a cost effective process of separating .sup.90 Y of sufficient quality and quantity without a series of .sup.90 Sr selective extraction chromatographic columns while minimizing loss of .sup.90 Sr and without generating large amounts of waste and using large volumes of eluent.